Interstate 170 (I-170) is the designation for an interstate route in the St. Louis, Missouri metropolitan area. I-170, also known as the Inner Belt Expressway, is an 11.17-mile (17.98 km) highway traveling north-south through the St. Louis suburbs.

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I-170 was originally intended to provide an inner beltway within I-270 through St. Louis County extending to I-55 in the South County area;[2] however, the portion of the route south of I-64/US 40 was canceled due to local opposition. The portion of MetroLink's Cross County Extension south of I-64 runs roughly along the proposed alignment.[3]

The southern portion of I-170 was built using St. Louis County funds in the 1960s through a shallow valley. It was signed as Route 725.

The southern two interchanges on I-170 (at I-64/US 40 and Galleria Parkway) were reconstructed as part of the first phase of the New I-64 project. Most notably, the new interchange includes direct access to I-170 from eastbound I-64; however, access to Galleria Parkway from northbound I-170 was eliminated. Eager Road access to and from I-170 was also revised in the New I-64 project.[4]

Because Interstate 170 terminates at I-64/US-40, a direct access from Interstate 170 and Interstate 64 (Highway 40) to Interstate 55, Interstate 270, and Interstate 44 are lacked. Also, towns such as Richmond Heights, Brentwood, Maplewood, and Marlbourough lack access to the Interstates, the St. Louis Lambert International Airport, South County, and to each other. Because of this, commuters either have to take indirect surface streets as bypasses such as Hanley Road or River Des Peres Boulevard which would result in a much higher mileage and time due to traffic signals and a longer route. For example, if one is in Richmond Heights and wants to get to South County, they have to take Brentwood Blvd to Eager Road to Hanley Road to Murdoch Ave to I-44 and then to I-270 towards South County. This also results in higher traffic in residential streets and towns such as Shrewsbury.[5] Proposals had been made to solve this problem such as a new freeway for faster commute or “South County Connector” to connect Richmond Heights to South County but these proposals had been postponed due to lack of funding.[6]